In many uses and applications of photography it is desired to obtain greater detail than can be seen upon ordinary examination of a photographic film or print. Particularly in the type of photography that can be considered utilitarian rather than artistic, such as industrial or engineering uses and applications, medical photography and particularly X-ray photography, and in scientific and experimental operations seeking information from a picture, it is desirable to look for details in a picture which are hidden from normal visual examination. Typically, in many instances desired details in light picture areas and details in dark picture areas of the same photographic record may be hidden in the glare and in the shadow.
The present invention uses surface characteristics of a photographic layer to enhance or even to replace the photographic image which ordinary visual examination sees as density differences. Instead of seeing only or primarily different areas of black and white in which light is absorbed or reflected by the pressure or absence of black silver in a gelatin emulsion, the present invention utilizes surface characteristics of a photographic layer such as a conventional gelatin emulsion with a developed silver image. Previous efforts to use the surface or relief characteristics of photographic emulsions have been unsuccessful except in certain specific cases such as microscopic examination of extremely small areas of the photographic image.
It is well known that differential tanning and other effects produce a surface relief on photographic emulsions such as silver halide gelatin or similar emulsions, and it is known that the surface relief or surface perturbations in such emulsions are greater in areas where there is a changing photographic density in the image and lesser in the areas where there is a constant or nearly constant density. In particular, in relatively uniform dark areas and in relatively uniform bright areas the densities may be extreme, and the shadows and glare consequently very strong, but the surface characteristics in such areas show perturbations where there are less visible differences corresponding to details within such areas.